Electron discharge device



March 9, 1937. H. KNIEPKAMP ELECTRON DISCHARGE DEVICE Filed April 6,1935 Reg 1 INVENTOR. HEINRICH KNIEPKEMP wwzm ATTORNEY.

Patented Mar. 9, 1937 UNITED STATES PATENT OFFICE- ELECTRON DISCHARGEDEvicE many Application April 6, 1935, Serial No. 14,971 In GermanyDecember 23, 1933 1 Claim.

My invention relates to electron discharge devices, and moreparticularly to grid actuated hot cathode vapor tubes or vaporconvertors.

In thermionic electron discharge tubes the tem- 5 perature of thecathode has little effect on the saturation current, although owing tothe shortening of the active length of the cathode as a result of thecooling action at the ends, the slope of the current-voltage curve maybe aifected to a certain degree. However, the operating conditions ofsuch a tube are substantially a function of the well-known space-chargelaw.

In the case of gasor vapor-filled discharge tubes in which a controlaction is obtained by the selecting or fixing the point at which theignition or gas discharge is initiated, which is termed the breakdownvoltage, the temperature of the cathode has a very pronounced effect. Inthe non-conducting or static state, that is when no discharge current isflowing through the discharge tube, the control electrode or controlelectrodes are so adjusted that no electrons, or only a few electronsproduced by the cathode will be able to reach the space between theanode and the control electrode. If this space does not contain anyelectrons, then, for given electrode dimensions and spacings, and at theexisting gas pressure, no ignition or starting of the discharge willoccur. The ignition or breakdown will be brought about only at theinstant when the num oer of the electrons entering the space between theanode or plate and the control electrode has reached a certainmagnitude. The entrance of these electrons and their number however, de-

pends not only upon the resultant field of the anode and the controlelectrodes, but also upon the initial velocities of the electrons, andthis factor is in turn a function of the temperature of the cathode. Incontradistinction to highvacuum tubes, initiation of ignition ordischarge in the case of gas-filled tubes is dependent upon thesaturation current of the cathode. This accounts for the markeddependence of the ignition characteristics of tubes of this kind on thetemperature of the cathodes. Thus, all tubes of this kind are dependentto a large degree upon cathode filament or cathode heater voltagefluctuations of the supply-line. Inasmuch as the line voltage,especially where long-distance transmission networks are concerned, is,at times, temporarily subject to serious fluctuations amounting often to10% and more, such voltage variations mean an aggravation of thedifliculties of operating gas-filled tubes.

The same effect brought about by fluctuations in the heating potentialis also caused by residual ions inasmuch as the presence of suchresidual ions will affect to varying degrees the electrons emitted bythe cathode. The effect of the residual ions is particularly pronouncedin connection with the use of hollow cathodes of the kind extensivelyand preferably employed in electron discharge tubes designed to handleheavy currents.

The influence of fluctuations of the supply-line potential and thus thevariations of the cathode temperature is still more marked in theoperation of tubes having two or more control or auxiliary electrodes.

The object of this invention is to provide a gaseous discharge tubehaving one or more control electrodes in which the voltage fluctuationsof the supply-line and the resulting variations in the temperature ofthe cathode will not affect the operating characteristics of the tube.

This object is attained by providing control electrodes havingpredetermined dimensions and spacings so that the effective fields ofthe various electrodes on the cathode bear a predetermined relationshipto each other.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claim, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawing in whichFigure "l is a diagrammatic representation of a gaseous discharge tubeembodying my invention and associated circuits, and Figures 2 and 3 aregraphical representations of the operating current and voltagerelationships of the tube and circuit shown in Figure 1.

Figure 1 shows the fundamental circuit diagram of a tube having a gas orvapor atmosphere and provided with two control grids. The tube containsa thermionic cathode it, an anode a and two control electrodes gl andg2. Between cathode k: and anode a. is applied an alternating voltagelta, between grid gi and the cathode is applied an alternating voltageugl of constant amplitude and lagging in phase by an angle of degreesand between the cathode is and the grid g2 is applied a variablealternating voltage u z presenting a. phase displacement angle ofdegrees with respect to voltage 169,.

In Figure 2 the voltage time relationships are graphically shown, thehorizontal axis representing time and the vertical axis the voltageatany particular time. It will be observed that the voltage 7131 appliedto grid gt is 90 degrees out of phase to the voltage applied to anode awhereas the voltage u z applied to grid 92 is 180 degrees out of phasewith the anode voltage. The curve marked I represents one value ofvoltage applied to grid 92 whereas curve II represents another value ofvoltage applied to grid 92. The effect of the application of these twodifferent voltages is graphically shown in Figure 3. The horizontal andvertical axes in Figure 3 represent the time and voltage, and the curvemarked Ia represents the critical grid voltage, that is the voltage atwhich the tube will break down if the voltage represented by curve I inFigure 2 is applied to grid g2, the voltage represented by Hg], inFigure 2 being applied to grid of, and the voltage represented by usbeing applied to the anode. Similarly if the voltage represented bycurve II in Figure 2 is applied to the grid 92 the critical gridvoltages are as represented by the dotted line 11a, that is if anyvoltage is applied to the grid 9! corresponding to Ho the tube willbreak down and the discharge occur with voltages corresponding to usbeing applied to the anode. If voltage ugl in Figure 3 applied to gridyl has the value at some time tl as represented by the intersection ofthe curve ugl and curve Ia then the tube will break down at point A anda discharge occur at tl. Likewise, if the voltage IIa is applied to thegrid 92 the discharge will occur at time t2 represented by theintersection of ug2 and dotted line 11a in Figure 3 at the point B.Thus, with the arrangement above described it is possible to change thetime at which ignition or discharge will occur by varying the voltageug2 which is applied to grid 92 and thus control the mean value of thealternating current at which break down will occur.

As has been pointed out above, ignition will occur whenever .asufficient number of electrons happen to get from the cathode into thespace in front of the anode or plate. An adequate number of suchelectrons will not enter if the resultant field of anode a, grid gl andgrid g2 is such that electrons coming from the cathode are blocked. Ifthe speed of the electrons emerging from the cathode were zero, then apotential of zero of the resultant field would suffice. However,inasmuch as the electrons have, as a matter of fact, a certain rate ofvelocity ranging between 1 and 2 volts, it will be seen that theresultant voltage of the combined or resultant field between the cathodeand grids and anode likewise must amount to about 1 to -2V in order thata blocking action may be produced. The resultant field of anode a, gridgl and grid g2 or the resultant voltage 11st in the light of the knownlaws of electrostatics is given by this relation:

D1 represents the voltage effect of the plate field across the grid yl,while D2 represents voltage effect of the composite field of anode a andgrid 9| through the grid 92. In the presence of a constant filamenttemperature the critical value of st is a constant, and at about 800degrees C. cathode temperature it is about 2V. The harmful influence ofvoltage variations and of the ensuing temperature fluctuations of thecathode, according to the present invention, in the case of an electrondischarge tube containing an anode, an electron source, at least twocontrol elements as well as a gas or vapor atmosphere is diminished byhaving the anode field thru the grid yl located closest to the anode(factor D1) not more than one-tenth as effective as the field of anode aand grid yl across the grid 92 closest to the cathode (factor D2) incontrolling the flow of electrons from the oathode to the plate.Expressed in another way the amplification factor of grid gl withrespect to the anode is only one-tenth as great as the amplificationfactor of. grid 92 with respect to grid yl and the anode. If theresultant voltage effect of the combined fields between the cathode andthe other electrodes within the electron discharge device is representedby 100% then it has been found in practice that the grid g2 must be sodesigned and dimensioned that the resultant voltage effect of thecomposite field of anode a and grid gl thru the grid 92 (factor D2),should amount to 50% or over of the resultant voltage eifect of thecombined fields of all the electrodes while the voltage effect of theanode field thru the grid gl (factor D1) should vary between 1 and 3% ofthis resultant voltage.

This invention is directed not only to an electron discharge device withtwo control electrodes or grids but it will be found applicable inconnection with tubes having a larger number of control electrodes.

While I have indicated the preferred embodiments of my invention ofwhich I am now aware and have also indicated only one specificapplication for which my invention may be employed, it will be apparentthat my invention is by no means limited to the exact forms illustratedor the use indicated, but that many variations may be made in theparticular structure used and the purpose for which it is employedwithout departing from the scope of my invention as set forth in theappended claim.

What I claim as new is:\

An electron discharge device having an envelope containing a gas orvapor atmosphere, a cathode, a first and second control grid, and ananode spaced from said cathode, said first control grid having anamplification factor with respect to said second control grid and anodewhich is ten times as great as the amplification factor of said secondcontrol grid with respect to said anode.

HEINRICH KNIEPKAMP.

